This study will continue to evaluate the efficacy of naltrexone as an adjunct to treatment for alcohol dependence. Findings from our 12-week, double blind study comparing 50 mg. per day of naltrexone or placebo in 70 male alcoholics in outpatient rehabilitation provides support for the efficacy of naltrexone revealing that relative to subjects receiving placebo tablets, the naltrexone group reported less alcohol craving, fewer days in which alcohol was consumed, fewer days of intoxication, and had lower liver enzyme tests and much lower rates of alcohol relapse. The proposed study constitutes a more comprehensive, large scale extension of our earlier research using a heterogeneous population of men and women. Specifically, we will assess for what subgroups of alcoholics and for what duration of treatment is naltrexone an effective adjunct. Thus, one hundred-eighty alcohol dependent rehabilitation outpatients will be randonly assigned to either adjunctive naltrexone for three months, naltrexone for nine months, or to a placebo treatment in a double blind design extending over a nine month period. The larger N in this study, in addition to providing sufficient power necessary for the determination of group differences, will also permit subgroup analyses. A secondary aim of this study will be to attempt to determine whether there are psychiatric subgroups of patients that are particularly helped by naltrexone. Recent evidence suggests that alcohol dependent patients with significant psychopathology may have a worse prognosis than non-psychiatrically impaired patients. Preliminary data from our first study supports this observation with relatively high relapse rates in so called "dual-diagnosis " patients. In contrast, naltrexone treated subjects had a remarkably low relapse rate in this subgroup. A final aim of this study will begin to study the mechanism of action of naltrexone. Animal research suggests that naltrexone may decrease alcohol drinking because of its pharmacological effects of blocking opiate receptors. Preliminary data, from our initial study shows that among subjects who slip, that is have any alcohol during the twelve week active medication phase, naltrexone significantly blocks the high from alcohol. Based on our preliminary data, we hypothesize that naltrexone will block the pleasurable effects of alcohol and reduce craving only in those subgroups of subjects who sample alcohol.